An impact wrench is one illustrative embodiment of an impact tool, which may be used to install and remove threaded fasteners. An impact wrench generally includes a motor coupled to an impact mechanism that converts the torque of the motor into a series of powerful rotary blows (i.e., impacts) directed from one or more hammers to an anvil coupled to an output shaft. In a ball-and-cam type impact mechanism, the hammer both rotates about an axis and translates along that axis to impact the anvil. The translation of the hammer (and, hence, the timing of the impacts with the anvil) is mechanically controlled by one or more balls disposed in cam grooves formed between the hammer and a camshaft, as well as a spring that biases the hammer. After each impact with the anvil, the hammer rebounds rotationally around the axis and also translates backward along the axis due to the ball(s) and cam groove(s).
In a typical ball-and-cam impact mechanism, the design and size of the components (e.g., the spring, balls, and camshaft grooves) are often critical to efficient operation across a broad range of joints. For example, impact tools designed to operate on soft joints (i.e., low rebound applications where the majority of the impacting energy is transferred into the joint) often result in significant vibration of the impact tool when operating on hard joints (i.e., high rebound applications) due to the motor operating at higher speeds. Conversely, impact tools designed to operate on hard joints often perform inadequately on soft joints due to the motor operating at lower speeds.